Scotland – Flying on Borrowed Time

Wrapping up the Scotland-themed series, and launching off from last week’s grouse blog, today I’ll be discussing the persecution and decline of raptors in the UK (particularly in Scotland). When I say ‘raptor’, I’m unfortunately not referring to large theropod dinosaurs with killing claws. In this case, the word is a catch-all for any bird in the orders Accipitriformes (hawks, eagles, vultures, kites, etc.) and Falconiformes (falcons and caracaras). Worldwide there are more than 300 species, with 14 species occurring somewhat regularly in the UK and a further 13 being occasional vagrants. Raptors are a critical part of any ecosystem in which they occur, taking on numerous important roles including scavenger (such as vultures), pursuit and ambush hunters (gyrfalcon and peregrine, respectively), and apex predators (large eagles almost exclusively fill this role). They clean up detritus left by other carnivores, moderate the populations of species lower on the food chain through their depredations, and through this impact populations of other predators.

Unfortunately, this has made them somewhat unpopular in many circles, with gamekeepers being particularly susceptible (many raptors do prey on their charges, after all). In the UK, raptors have been persecuted since at least the 1400s, although the issue became increasingly widespread through the Georgian and Victorian eras as blood sports grew in popularity. In 1954, the Protection of Birds Act rendered it illegal to kill, injure, or remove any wild bird, or damage or destroy their nests and eggs. While some species, like buzzards, experienced a population upturn due to this, persecution still continued in some areas – most frequently in the off-the-grid, inaccessible grouse moors of upland Scotland. In some cases, population declines have been severe and unrelenting, with a number of species barely clinging on.

 

Hen harrier
A male hen harrier carries nesting material. Credit: RSPB

Grey Ghosts

The hen harrier, Circus cyaneus, is a mid-sized raptor in the same family as hawks and buzzards, Accipitridae, distributed across Europe and Asia. In some parts of its range it is a summer migrant, but across most of Britain it is a resident. Known for its habit of predating gamebirds, including chickens and grouse, the hen harrier typically breeds on upland moorlands, where it makes its nests among the leggier heather.

This combination of factors has been the major reason behind the hen harrier’s historical decline. Breeding on grouse moors makes it vulnerable to human interference, and its significant depredations on red grouse quickly incurs the wrath of gamekeepers and estate owners. Once widespread, the most recent survey (in 2010, so somewhat outdated), estimated 670 pairs in the UK, with the vast majority of these breeding in Scotland. It is often ‘managed’ ruthlessly on grouse moors, with at least 30% of breeding attempts failing due to human intervention, and up to 15% of Scotland’s population of females killed each year [1]. It’s only thanks to the surplus of females fledged from nests in other habitats that the population is able to persist. The situation is even direr in England, where hen harriers were once widespread in upland areas such as the Lake District, Bowland Fells, and the North York Moors. In recent years, only a handful of pairs have managed to breed successfully, with the species well on its way to disappearing entirely from its last strongholds. Wales, however, provides a glimmer of hope: contrary to the national pattern, hen harrier populations in northern Wales actually increased 33% between 2004 and 2010 – possibly due to the low human population density, and a reduced focus on driven grouse shooting when compared to Scotland and northern England. It’ll take a big shift in public perception (and the number of MPs and Lords with vested interests in grouse shooting), but hopefully we can bring about a similar reversal across the rest of the country, before it’s too late.

 

Golden eagle
A juvenile golden eagle swoops in. Credit: Peter Cairns/RSPB

Aerial Emperors

The golden eagle, Aquila chrysaetos, was once the UK’s largest bird of prey (until the successful reintroduction of the even larger white-tailed eagle – more on that later). Even the juveniles, distinguishable from mature birds by the large expanses of white on their wings and tails, are breath-taking in flight. However, to maintain such a large body, golden eagles need plenty of large prey, actively hunting many mammal and bird species, and relying on carrion to make up the deficit in winter. This, in turn, requires the eagles to maintain huge territories – up to 150 km2 per individual, about the size of Liechtenstein. This, unfortunately, makes them somewhat more vulnerable to disturbance and human interference than other raptors.

Much like hen harriers, golden eagles have experienced a dramatic population decline in the last few centuries. Once spread throughout the upland and mountainous areas of the British Isles, it is now entirely absent from Wales and Ireland, with the only stronghold left in the Scottish Highlands. In England, a small population clung on in the Lake District for a while, but as of 2016, when the final male failed to show in spring, is presumed to be extinct there as well. This leaves only 440 pairs of birds in the UK, along with some juveniles and unmated mature birds.

As with almost all raptors, the primary reason behind this decline is human interference. Poor and unsuitable landscape management can lead to fragmentation of the habitat the eagles hunt in, leading them to expand their ranges or go hungry, a problem compounded by the removal of large animal carcasses (such as those of red deer). The primary cause of their decline, however, is direct persecution on grouse moors – red grouse are frequently targeted by hunting eagles, though not as often as by hen harriers. Due to their tendency to scavenge, golden eagles are often baited with poisoned carcasses, which have the added ‘benefit’ of removing other birds which eat grouse and their eggs, such as buzzards and corvids. In recent years, satellite tagging of golden eagles has revealed the extent of this problem – of all the eagles tagged in the last twelve years, almost a third have vanished mysteriously over grouse moors, their tags suddenly ceasing to function [2].

Species like the golden eagle, which typically only fledge one chick per breeding season, and can take several years to reach maturity (these are known as K-selected species), are very vulnerable to low populations – often crossing some invisible threshold after which population dynamics change and extinction is virtually assured. They also take a long time to recover from declines, so chances of golden eagles returning to mountains south of the Scottish border are slim, unless this occurs through a reintroduction programme.

 

Peregrine
A peregrine shoots overhead. Credit: Pete Blanchard

Speeding Bullets

The peregrine, Falco peregrinus, is well-known as the fastest animal in the world, able to exceed 320 km/h when stooping after prey. Though they are fairly cosmopolitan in their distribution, peregrines require large open spaces for hunting, and cliff faces for safely nesting on (although many have found that skyscrapers make suitable alternatives). Like many falcons, the peregrine is well-adapted for catching avian prey in flight, preferring to target dumpier birds like pigeons and red grouse. This, naturally, has made them much-maligned within the grouse shooting community.

Over the last century, peregrines have had a fairly rough time of things, being one of the species most heavily-hit by the usage of DDT in the mid-1900s. DDT was widely used as an insecticide in the decades following WWII, applied indiscriminately to fields of crops to boost yield. Unfortunately, DDT is difficult for animal digestive tracts to break down, so it bioaccumulates up food chains – thrushes and pigeons eat the affected insects, and peregrines prey on these birds, increasing the amount of DDT contained in their bodies. While the insecticide has little impact on the adult birds, it becomes incorporated into the structure of their eggshells, weakening them to the point that they cracked during incubation. Such was the scale of this issue that the peregrine entered a steep population decline, with the majority of breeding attempts failing. Fortunately for the falcons, the source of the breeding difficulties was detected in time, and DDT was banned. In the following decades the population began to recover, and the UK now sits pretty with 1,500 pairs – about 20% of the entire European population. Unfortunately, their taste for grouse has made peregrines yet another target for ‘management’ on shooting moors. Adult birds are often shot down, and despite their inaccessibility, about a quarter of nests fail after human disturbance. Still, if their recent recovery is any indication, sufficient protection should allow the falcons to regain their historical numbers.

 

Rest, Recovery and Reintroduction

The Protection of Birds Act may have been the saving grace for some raptors, but it came too late for others. White-tailed eagle and osprey both vanished as breeding birds in the early 1900s, shot and collected to extinction (although osprey did continue to pass through the country on migration to Scandinavia). Red kite became extinct in England and Scotland in the 1870s, with only a handful of pairs surviving in central Wales. All three of these species, however, mark great conservation triumphs, with conservation schemes and reintroduction programmes having established successful breeding populations.

Red kite
A red kite circles. Credit: Martin Webb

The red kite, Milvus milvus, was once incredibly populous in the UK – accounts from the middle ages reveal that they were even common in London, feeding on human waste and discarded meat. After the 1500s, however, the kites were views as vermin, and relentlessly persecuted; combined with the introduction of proper sewage systems, the red kite declined precipitously, becoming extinct in England (1871) and Scotland (1879). Numbers in Wales dropped extremely low, with only a few pairs surviving in old oak woodland, all descended from a single female. This genetic bottleneck resulted in high levels of inbreeding, which kept the population from growing successfully until the 1960s. Even then, the Welsh population remained small and slow-spreading – but thanks to programmes run by the RSPB, Natural England, and Scottish Natural Heritage, the kite was successfully reintroduced to areas across its historical range. In recent years the red kite has begun to spread outwards from its strongholds at the reintroduction sites, with 1,600 pairs across the country, and some even turning up in gardens.

Osprey
An osprey goes fishing. Credit: Joe Pender

The story of the osprey, Pandion haliaetus, is not so bright. Persecuted for its fish-eating habits, and under siege by Victorian egg collectors and taxidermists, the osprey was pushed to extinction in England and Ireland in the early 19th Century, with the Scottish population following suit in 1916. Birds continued to pass through the country on their annual migration between Africa and Scandinavia, but it took almost forty years until a pair attempted to breed at Loch Garten in the Scottish Highlands. Their first nest failed due to egg collection, but they managed to breed successfully the following year, once a guard was placed on the nest. In the following decades the natural recolonisation continued, bolstered by the introduction of European birds to other sites in Scotland and England. In a dramatic turnaround, between 200 and 250 pairs are now estimated to breed in the UK.

White-tailed eagle
A white-tailed eagle shows off its size. Credit: Neil Higginson

Perhaps even more iconic than the return of the ospreys, is the successful reintroduction of the white-tailed eagle, Haliaeetus albicilla, now the UK’s largest bird of prey. Once fairly common in coastal areas of Scotland and Ireland, and also breeding in England and the Isle of Man, their eventual decline and extinction was rapid. Unfairly persecuted by shepherds and gamekeepers (these eagles mostly eat fish, rather than gamebirds or livestock), and by egg collectors and taxidermists, the white-tailed eagle disappeared from England by 1800. The Irish population reached extinction soon after, and by 1918, the last surviving eagle was shot in Shetland. After almost sixty years of absence, 82 young birds from Norway were released into the Scottish isles between 1975-85. Successful breeding occurred every year from 1985, and another injection of European birds in 1990 ensured that the population became self-sustaining. Now a relatively common site on Skye, Mull, and the other Hebridean islands, another reintroduction programme is attempting to build a separate population on Scotland’s eastern coast.

 

Until next time,

Jon

 


[1]        Etheridge, B., Summers, R.W. and Green, R.E. (1997) The effects of illegal killing and destruction of nests by humans on the population dynamics of the hen harrier Circus cyaneus in Scotland. Journal of Applied Ecology 34(4), 1081-1105. http://www.jstor.org/stable/2405296

[2]        Whitfield, D.P. and Fielding, A.H. (2017) Analyses of the fates of satellite tracked golden eagles in Scotland. Scottish Natural Heritage Commissioned Report No. 982. http://www.snh.org.uk/pdfs/publications/commissioned_reports/982.pdf

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